The general construction and operation of combustion chambers or combustors in gas turbine engines is considered to be well known to those skilled in the art. The present invention is directed to a cold combustor wall which is used to line the hot combustor wall of a gas turbine engine for improving cooling by addition of impingement cooling jets.
Within the combustor, fuel fed through the fuel nozzle is mixed with compressed air provided from a high pressure compressor and ignited to drive turbines with the hot gases emitted from the combustor. Within the metal combustor, the gases burn at approximately 3,500 to 4,000 degrees Fahrenheit. The combustion chamber is fabricated of metal which can resist extremely high temperatures, however, even highly resistant metal will melt at approximately 2,100 to 2,200 degrees Fahrenheit.
As is well known to those skilled in the art, the combustion gases are prevented from directly contacting the metal of the combustor through use of a cool air film which is directed along the internal surfaces of the combustor. The combustor has a number of louver openings through which compressed air is fed parallel to the hot combustor walls. Eventually the cool air curtain degrades and is mixed with the combustion gases. Spacing of louvers and cool air curtain flow volumes are critical features of the design of the combustors.
The turbulence of combustion gases within the combustor leads to rapid degradation of the air film cooling adjacent the hot combustor walls. Particularly where the hot combustion gases are being redirected as in the large exit duct of a reverse flow combustor, the interaction between turbulent combustion gases and the cool air film along the hot combustor wall leads to rapid deterioration of the cooling air film. As a result, it is generally necessary to increase the volume and flow rate of cooling air in such critical areas. Introduction of cooling air may not be optimally efficient for the completion of combustion nor for the presentation of hot combustion gases to the turbines. However, for lack of a better solution, designers have conventionally accepted a degree of inefficiency caused by excessive use of cooling air film as a necessary part of combustor design.
It is an object of the invention to provide improved cooling for the hot combustor wall, particularly in the critical area of the large exit duct portion where rapid degradation of cooling air films is prevalent.
It is a further object of the invention to provide for relief of thermally induced stresses in the hot combustor wall to optimize the design of the combustor.
It is a further object of the invention to provide improved cooling efficiency for the hot combustor wall which permits the designer to compensate for deficiencies in conventional cooling systems and particularly to address local areas of the hot combustor wall which are not adequately served by conventional air film cooling systems.